720 SUIIMART OF CURRENT RESEARCHES RELATING TO 



palliftl commissures. The pcnial nerve arises near the right pallial, has 

 a large ganglion at the base of the penis, and remains ganglionic to 

 near its extremity. There is a small but distinct olfactory ganglion. 

 On the whole the nervous system is very much like that of Bithi/nla. 



The tcntaculiform filament is almost identical in structure with the 

 tentacle itself; like it, it has an axis of ramifying connective tissue, and 

 longitudinal and circular muscular bundles, but there is only one nerve in- 

 stead of two, and the blood-lacuna is very reduced. The genital organs arc 

 difficult to make out. The hermaphrodite gland jn-oduces eggs at the 

 periphery and spcimatospores at the centre; the oviduct has an important 

 dilatation, and receives the united products of the two albuminiparous 

 glands. Contrary to the statement of Moquin-Tandon, the author found 

 that the genital ducts were separated. 



The salivary and albuminiparous glands and all the pallial organs 

 Lave only one layer of epithelial cells, and the distinction between 

 ciliated and secretory cells may be f)bserved very distinctly. 



The zoological affinities of Valvnta are somewhat obscure, for the 

 various organs have points of resemblance to those of the most various 

 Gastropods. It is clearly enough a trenioglossate Prosobranch, but it is 

 an aberrant type in which some of the points of the organization of the 

 Diotocardia are retained, but it is not, strictly speaking, an intermediate 

 form. 



5, liamellibrancliiat?. 



Pericardial Gland.* — Prof. C. Grobben gives a full account of his 

 investigation of the but little-known pericardial gland of Lamcllibranchs. 

 His memoir discusses the structure of the organ, the occurrence of con- 

 cretionary deposits in other parts of the body, the function of the gland, 

 and its morphological relations. The chief results may be condensed as 

 follows : — 



The pericardial gland occurs in numerous Lamellibranchs as an 

 epithelial modification in two regions, namely, above the auricles and in 

 the anterior angles of the pericardium. In the first position it is in- 

 cipient in Area, well developed with processes in Peciuncidus, especially 

 large in MijtUus and Lithodomus, but tending to degenerate in the 

 Monomyaria — Peden, Spondi/Ius, Lima, Ostrea. It is more or less 

 markedly developed in Dreissena, Unto, Anodonta, Venus, Cardium, Scro- 

 hicidaria, Solen, Pholas, and Teredo. The glandular sacs formed by 

 invagination of the mantle lamellae in the anterior angles of the peri- 

 cardium occur in Unio, Anodonta, Vemis, Cardium, Scrohicidaria, Solen, 

 and Pholas, while in the series of Hcteromyaria and Monomyaria they 

 are exhibited by Breissena alone. In Pholas the openings of the pallial- 

 pericardial gland are lost, and the sacs exhibit a partial division, as is 

 also seen in the auricular glands of Area, Pectuncuhs, and Lithodomus. 

 In Meleagrina there are projecting tufts on the posterior margin of the 

 pericardial cavity. 



The epithelial cells of the pericardial glands of Area, Pectuncnhis, 

 Ml/tilus, and Lithodomus bear flagella and contain concretions. "When 

 richly laden with the latter they are thrown ofi", and most probably pass 

 to the exterior from the pericardial space via the kidneys. The function 

 is excretory and kidney-like. The dark colour seen even when the 



* Arbeit. Zool. Inst. Univ. Wicn, vii. (ISSS) pp. 355-444 (6 pis.). 



